1. Field of the Invention
The present invention relates to a process of purifying or decontaminating photographic processing effluents and recovering silver therefrom by applying photosynthetic sulfur bacteria to the photographic processing effluents. More particularly, the invention relates to a process of purifying or decontaminating photographic processing effluents containing reductive sulfur compounds, in particular, waste fix solutions for silver salt photographic materials, and recovering silver from such effluents or solutions separately or simultaneously by applying photosynthetic sulfur bacteria to these effluents or solutions under anaerobic conditions with light irradiation.
2. Description of the Prior Art
Many kinds of processing solutions for conventional silver halide photographic materials depending on the purpose of the processing are known but the most fundamental processing solutions for silver halide photographic materials are developers and fix solutions. A fix solution is an aqueous solution which is used for dissolving away silver halides present in silver halide photographic materials at the portions unexposed to light after development and a fix solution contains, as the main components, thiosulfates, sulfites, acetic acid, etc. Thus, a used fix solution contains the components described above in addition to solubilized silver thiosulfate complex salts. Consequently, in such a waste or used fix solution, the biological oxygen demand (BOD), the chemical oxygen demand (COD), and the total oxygen demand (TOD) which are indices showing the extent of contamination of waste solutions generally are very high. It is desirable to purify or decontaminate these waste fix solutions, that is, to reduce the above-described oxygen demands of waste fix solutions before these solutions are discharged in general. Of the above-described contaminants present in waste fix solutions, sulfur compounds represented, in particular, by thiosulfate ions (S.sub.2 O.sub.3 --) are the main consumer of oxygen and the amount of these compounds present in waste solutions is large. Therefore, a great need for an appropriate treatment of these components exists.
On the other hand, a developer is a processing solution which is used for reducing silver halides in the portions exposed to light of silver halide photographic materials to silver and a developer is usually an alkaline aqueous solution mainly containing developing agents such as hydroquinones, p-aminophenols, phenylpyrazolidones, p-phenylenediamines, etc., together with sodium sulfite. Thus, a waste developer also has a high BOD, COD and TOD.
Examples of other photographic processing solutions are a bleach solution, a processing solution for removing silver from developed siver halide photographic materials, a neutralizing solution, washing water, etc.